1. Field of the Invention
The present invention relates to controlling a flash memory, and more particularly, to a method and controller for managing a memory device.
2. Description of the Prior Art
Developments in flash memories have led to wide application in portable memory devices, such as memory cards conforming to the SD/MMC, CF, MS and XD specifications. How to control flash memories in these portable memory devices has become an important issue.
NAND flash memories include single level cell (SLC) memories and multiple level cell (MLC) memories. Each transistor in an SLC flash memory (which can be viewed as a memory cell) only has two electric charge levels representing logic 0 and logic 1, respectively. The transistors in an MLC flash memory are driven by a higher voltage to record information of multiple bits (e.g. 00, 01, 11, 10) using voltages of different levels. Theoretically, the recording density of the MLC flash memory can be more than twice the recording density of the SLC flash memory. This is good news for the manufacturers of NAND flash memories when considering issues in design and research.
Since the manufacturing cost of MLC flash memories is cheaper than that of SLC flash memories, and as the MLC flash memories may provide a larger capacity in a limited space, applying MLC flash memories to portable memory devices has become more and more popular. The operation of some types of MLC flash memories can be complicated, and introduces various issues. For example, the initialization time of a conventional memory device adopting an MLC flash memory will be greatly increased, making the related cost increase correspondingly. Hence, there is a need for a novel method to enhance the control of memory devices which can improve their initialization efficiency without introducing negative side effects.